Phytoremediation and high rainfall combine to improve soil and plant health in a North America Northern Great Plains saline sodic soil

Abstract

Saline/sodic soils are often remediated by applying gypsum, improving drainage, and irrigating with high quality water. However, these management approaches may not be effective or feasible in dryland soils supersaturated with gypsum. A field study, conducted between 2017 and 2021, investigated the effect of phytoremediation on soil and plant health in a landscape containing productive, transition, and saline/sodic soils. Phytoremediation treatments–corn (Zea mays) and two perennial grass mixes (mix 1 slender wheatgrass [Elymus trachycaulus] and beardless wildrye [Leymus triticoides], and mix 2 slender wheatgrass, creeping meadow foxtail [Alopecurus arundinaceus], western wheatgrass [Agropyron smithii], and green wheatgrass [Elymus Hoffmannii])–were planted and compared with a no-plant control treatment across three soil zones. Perennial grasses were dormant seeded in the winter of 2017 and 2018, and corn was grown in 2018, 2019, and 2020. Soil samples (0 to 15 cm) were collected on July 24, 2018, July 23, 2019, July 24, 2020, and April 15, 2021. Across soil zones, corn production was 5,990 (grain + stover), 3,900 (stover only), and 6,150 (grain + stover) kg ha⁻¹ in 2018, 2019, and 2020, respectively, whereas perennial grass biomass yields averaged 1,220, 9,065, and 7,375 kg ha⁻¹ in 2018, 2019, and 2020, respectively. Due to high rainfall that occurred from the fall of 2018 through the summer of 2019, the depth to the water table decreased and the soil electrical conductivity (EC1:1) (−0.83 ± 0.149 dS m⁻¹) and exchangeable sodium (Na⁺) (−656 ± 220) decreased in all treatments. In addition, from 2018 to 2019, the risk of soil dispersion (lower Na⁺/EC_1:1 ratio) was less in treatments with growing plants (p = 0.02) than plots without plants. With drier conditions from the fall of 2019 through the spring of 2021, the depth to groundwater increased, the EC_1:1 decreased in the transition soil but increased in the saline/sodic soil (p = 0.001), and the Na⁺/EC_1:1 ratio increased in the productive and transition soils and was static or decreased in the saline/sodic soil (p = 0.001). In conclusion, this and related work showed that phytoremediation when combined with high natural rainfall reduced soil EC_1:1 and the exchangeable Na⁺ in all soils; however, these benefits may be short lived, and as the water tables dropped in 2020, EC_1:1 increased in the saline/sodic zones. Laboratory and linked research from the study site also showed that fertilizing saline sodic soils can result in very high nitrous oxide (N₂O) emissions, and reseeding degraded soil to perennial plants provides soil cover that reduces the risk of erosion and provides habitat for wildlife.